We propose to determine the biologic importance of the human- bacterial-rat erythrocyte heterophile system to human renal transplantation. It involves studies of normal subjects, patients with acute infections, and patients with chronic renal failure before and after transplantation. The study should elucidate methods of acquiring sensitization to the system and the clinical significance of that sensitization. The distribution of heterophile antigens among human beings and bacteria and their relationship to renal allograft rejection will be determined.